Conventionally, when a semiconductor integrated circuit (IC) package is mounted on a circuit board, lead wires projecting from the side surface of the IC package are inserted into through-holes with lands of a circuit pattern on the circuit board. And the lead wires are electrically connected to the lands with solder. On the other hand, in recent years, the number of input-output terminals of the IC package is increasing with improvement of the integration density of the IC. Furthermore since operating frequency of the IC rises, there is a demand for improving the high-frequency characteristic of the circuit board. Therefore demands for high density mounting on the circuit board and short distance connection in the circuit board and narrow pitch mounting on the circuit board are increasing.
For example, techniques for providing the input-output terminals in a reticular pattern formed on the back side of the IC package such as BGA (Ball Grid Array) and LGA (Land Grid Array) and for mounting the IC package on the surface of the circuit board so as to dispose the input-output terminals efficiently under these demands are proposed. The surface mount technology that uses an interposer as an interconnecting board between the IC package and the circuit board is proposed. The interposer includes an insulation material sheet and a conductor (for example, connector). The insulation material sheet has through-holes corresponding to input-output terminals formed in a grid-array pattern on the IC package. And the conductors are inserted into these through-holes to conduct electrically in vertical direction of the insulation material sheet. Terminal patterns arranged in a grid-array pattern that is similar to that of the IC package are formed on the circuit board. It is illustrated using FIG. 1 to mount the IC package on the circuit board using the interposer.
FIGS. 1A to 1C illustrate a conventional interposer. FIG. 1A illustrates that an interposer 2 is disposed between a circuit board 3 and an IC package 1. Moreover, FIG. 1B illustrates a side view of FIG. 1A, and especially a cross-sectional view of the interposer 2. Input-output terminals 4 (electrodes) are provided in a grid-array pattern formed on the back side of the IC package 1. And for mounting the IC package 1 on the circuit board 3, each of terminal patterns 6 (electrodes) is formed at position corresponding to each of the input-output terminals 4.
The interposer 2 is disposed between the IC package 1 and the circuit board 3, and connects the input-output terminals 4 on the back side of the IC package 1 to the terminal patterns 6 on the circuit board 3. The interposer 2 has a plurality of through-holes 9, which are formed into the insulation material sheet (hereinafter called an interposer substrate) 8. Each of the through-holes 9 corresponds to each of the input-output terminals 4 in the grid-array pattern formed on the IC package 1. A connector 5 is inserted into the through-hole 9. Each of the connectors 5 is the same length, and the connector 5 is made of the conductive material that electrically conducts between the front side and the back side of the interposer substrate 8.
The interposer 2 is generally disposed inside a socket 7 illustrated in FIG. 1C, and the socket 7 is mounted on the circuit board 3 by soldering. When the socket 7 is used, the IC package 1 is easy to mount and demount on the circuit board 3.
In the interposer 2 as mentioned above, the structure of the connector 5 that is made of the conductor which conducts electricity between the front side and the back side of the interposer substrate 8 is important. The connector 5 is placed and compressed between the input-output terminal 4 on the back side of the IC package 1 and the terminal patterns 6 on the circuit board 3. Therefore the connector 5 has elasticity to conduct electricity between the IC package 1 and the circuit board 3 while being compressed under pressure from both the IC package 1 and the circuit board 3.
As a structure to provide elasticity to the connector 5, Japanese Laid-open Patent Publication No. 2001-176580 (hereinafter called “patent document 1”) discloses the connector that includes a flexible conductive element wound around the compressible insulating core and a compressible elastic outer shell the surrounding the conducting element. The patent document 1 also discloses that the outer shell is an elastic body such as rubber, and that the outer shell surrounding the core is surrounded by an insulating layer made of a conductive wire mesh or a continuous metallic layer.
However, as a structure to provide elasticity to the connector 5, the patent document 1 discloses the structure that builds a zigzag wire, a pleat wire or a coiled wire into the main body of the elastic body, and discloses the structure that builds a metallic spring into the main body of the elastic body. However, there is a problem that the structure disclosed in the patent document 1 physically has the limit of downsizing. Moreover, there are problems that the structure disclosed in the patent document 1 is complex and causes high cost.
FIGS. 2A to 2D illustrate a conventional connector. As the solution of the problems described above, the connector 50 that has an elastic connection body 52 illustrated in FIG. 2A is proposed. The connector 50 has the elastic connection body 52 that includes a U-shape conductive spring 53, and the connector 50 is fitted in a through-hole 9 of the interposer substrate 8 as illustrated in FIG. 2B.
Both ends of the spring 53 of the elastic connection body 52 are contact parts 54 and 55. As shown in FIG. 2C, when an interposer 80 is disposed at a predetermined position on the circuit board 3 and the IC package 1 is mounted on the interposer, the contact part 54 contacts the input-output terminal 4 of the IC package 1 and the contact part 55 contacts the terminal pattern 6 of the circuit board 3. Consequently, the pressure received from the IC package 1 and the circuit board 3 is absorbed as the spring 53 is bent.
FIG. 2D illustrates an interposer 70 including a connector 60 with a similar structure to the connector 50 described in FIGS. 2A to 2C, and it is described in U.S. Pat. No. 4,969,826 (hereinafter called “patent document 2”). The interposer 70 includes an interposer substrate 68 having through-holes 69 and the connector 60 provided in the through-holes 69. A contact 65 is provided in a housing 64 of the connector 60. The contact 65 includes two contact parts 61 and 62 and a spring 63 that connects between the contact part 61 and the contact part 62. The contact parts 61 and 62 protrude from the top surface and the bottom surface of the interposer substrate 68 respectively. The contact part 61 contacts with the input-output terminal 4 of the IC package 1 and the contact part 62 contacts with the terminal pattern 6 of the circuit board 3 as well as the structure of the connector 50 described in FIGS. 2A to 2C.
However, as illustrated FIGS. 2A to 2C, the interposer 2 in which the U-shape conductive spring 53 is built has some problems. There are problems that a downsizing of the interposer 2 is limited to secure a prescribed deformation amount of a metallic spring, a design of the interposer 2 is difficult, and an electric resistance of the interposer 2 is large because a current pathway is long. FIG. 7A illustrates relation between deformation amount of the connector and contact pressure of the connector. In FIG. 7A, P in y-axis indicates contact pressure of the connector, A in y-axis indicates a range of the contact pressure, D in x-axis indicates deformation amount of the connector and B indicates a range of the deformation amount. As disclosed in the patent document 2, there is a problem that the range of the contact pressure corresponding to the range of the deformation amount in the contact part is large, that is, the variation of the contact pressure is large, as illustrated in FIG. 7A.